The present invention relates to fluid coupling devices, particularly of the type having both a fluid operating chamber and a fluid reservoir chamber, as well as valving which controls the quantity of viscous fluid in the operating chamber.
Although the present invention may be used advantageously in fluid coupling devices having various configurations and applications, it is especially advantageous in a coupling device of the type used to drive a radiator cooling fan of an internal combustion engine, and will be described in connection herewith. It is to be understood, however, that the present invention can be used with other accessories or components and in industrial applications, rather than just with vehicles, such as automobiles and trucks.
Fluid coupling devices of the viscous clutch type, have been used for many years for driving engine cooling fans (thus called “fan drives”). Such fan drives can result in substantial savings of engine horsepower and thus can increase the amount of miles of travel that the vehicle can achieve per gallon of fuel. The typical fluid coupling device operates in the engaged, relatively higher speed condition only when cooling is needed, and operates in a disengaged, relatively lower speed condition when little or no cooling is required.
Electrically activated viscous fan drives are known and used today because they can be precisely controlled between an engaged, partially engaged, and disengaged mode to control output at a given fan speed as determined by the vehicle's engine computer.
The electrically actuated viscous fan drives in use today have the actuator mounted to either the front or rear sides of the fan drives. In both cases, the actuators are mounted to the drives with ball bearings and the electrical wires are tethered to a stationary location on the engine or shroud or whatever optimum location is appropriate for the particular vehicle or customer application.
For front-mounted actuators the length of the electrical tether (wire harness) is a limiting factor for large fan applications. For rear-mounted actuators, the axle length can limit usage in narrow package applications. In addition, they also require a tether (wire harness) from the fan drive to a stationary location that can be difficult to install in the vehicle if the fan is assembled to the fan drive before installation. The durability of either design is a function of the bearing life as well as the durability and life of the tethered electrical wires and/or brackets.
Thus, a fan drive without a tether, that is without electrical wires tethered to a stationary location, and without actuators mounted to ball bearings, could improve the durability of the fan drive, as well as lower the cost of the fluid coupling drive. It is also important, however, that the tetherless fan drive maintain the same or similar fan drive performance characteristics and attributes as the tethered fan drive.
The front-mounted electrical actuator fan drive was the result of an evolution of earlier air-actuated viscous fan drives used in heavy truck and large bus applications. Initially, bi-metal control spring members and mechanisms were utilized on the front of the viscous drives. These were subsequently replaced by bearing-mounted pneumatic solenoids. Durability issues with the tethers and higher fuel economy requirements demanded by the public and government entities forced the heavy-duty industry to switch to pneumatic on/off friction clutches without a tether. In these clutches, the air supply was supplied through the center of the mounting brackets-pulley subassembly.
Today, the automotive and heavy-duty industry is facing even stiffer fuel economy restrictions, as well as noise control requirements. These continue the need for variable speed or at least multi-speed fan drives. As a result, viscous drives are economical and durable solutions that have evolved to the use of rear-actuated viscous fan drives. These rear-mounted electrically controlled actuators were developed to reduce potential tether durability problems associated with front-mounted style actuators.
Front actuated viscous fan drives continued to be used for light to medium duty applications because the axial length and cost are better than rear actuated fan drives. However, in some light duty gasoline engine applications where the fan clutch is driven by the water pump, a system resonant problem exists caused by numerous factors including the mass center of gravity (CG) of the fan drive.
Thus, a new and improved viscous fan drive is needed for numerous applications, whether for light, medium duty or heavy vehicle usage. In addition, the need exists for actuators having reduced costs, improved durability, and better noise and vibration performance.